Bright treatment for workpieces having toxic carryover



United States Patent 3,475,219 BRIGHT TREATMENT FOR WORKPIECES HAVINGTOXIC CARRYOVER Leslie E. Laney, Ellwood City, Pa., assignor to LaneyLaboratories, Erie, Zelienople, P2,, a corporation of Pennsylvania NoDrawing. Filed July 12, 1966, Ser. No. 564,550 Int. Cl. 1508b 7/04, 1/02U.S. Cl. 13427 4 Claims ABSTRACT OF THE DISCLOSURE An aqueous chemicalneutralizing solution containing an alkaline metal hydroxide andpermissibly soda ash and a high concentration of chlorine having arelatively high pH of 8 to 14; it also contains .1 to 1 g./l. ofbenzotriazole. The solution is applied directly to an acid or cyanidecarry-over on workpieces having copper or silver surfaces to immediatelyform a protective coating on such surfaces and to maintain such coatingthroughout the full neutralization of the toxic carry-over andsubsequent water rinsing of the surfaces.

This invention relates to the treatment or conditioning of aqueoussolution carry-over, such as adheres to metal workpieces or articles,for removing or neutralizing its toxic material content. A phase of theinvention deals with maintaining workpieces having easily tarnished oroxidized metal surfaces in a bright condition or inhibiting theiroxidation while quickly and effectively conditioning the aqueoussolution carry-over to make it non-toxic or innocuous. Another phase ofthe invention deals with an improved toxic carry-over conditioningsolution.

A problem has been presented from the standpoint of complexity and sizeof equipment required, cost of materials, the time element and thedifficulty of completely conditioning toxic solution carry-over having acyanide or acid content, without tarnishing or oxidizing copper, copperalloy or silver surfaces of the metal workpieces. The need has been fora procedure or approach to the problem which will enable a conditioningsolution to be recirculated and the workpieces to be moved in-line, inthe manner shown in US. Patent No. 2,725,314, from a previous processingtreatment bath through a toxic carryover treating bath, without thenecessity of stopping the movement of the workpieces or greatlyincreasing the size or length of the bath container, and in such amanner as to fully treat the carried over solution without damaging ortarnishing the highly susceptible surfaces of the workpieces. Thedifficulty has been to provide some approach to the problem that willmeet all the factors involved; that will not adversely effect theremoval or neutralizing procedure or cause surface staining of theworkpieces, e.g., from the standpoint of adverse reaction with thechemicals or the reaction products of a neutralizing solutionconditioning of the toxic carry-over, of makingreconditioning-recirculation of the solution impractical, of limitingthe concentration of the conditioning chemicals, of requiring anincreased time period to complete the removal of the toxic material suchas to make continuous in-line treatment impractical, and from thestandpoint of surface-oxidizing difficulties during movement of theworkpieces to a water washing or rinsing station or at such station.

Copper plated or cuprous alloy, brass or silver plated workpieces whichhave been subjected to a cyanide-type of plating, etching or treatingsolution, and workpieces having copper or cuprous alloy surfaces whichhave been subjected to acid pickling, acid brightening, or acid platingprocessing, have a toxic chemical solution carry-over that should bechemically treated to render the solution 3,475,219 Patented Oct. 28,1969 "ice innocuous prior to passing the workpieces through a waterrinsing bath or before their processing has been completed. A treatmentof copper, copper alloy (including brass) and silver surfaces ofworkpieces that have been subjected to a cyanide-type plating process isto rinse them in a solution containing an alkaline metal hydroxide, suchas caustic soda, to provide a pH of about 8 to 14, with the introductionof chlorine to oxidize the cyanide. However, it has been determined thatfor a complete treatment of the carried-over aqueous solution (noresidual cyanide), it is desirable to maintain a chlorine concentrationof a minimum of 500 mg./l. up to a maximum of about 2000 mg./l.

It has been discovered that although a chlorine concentration of about100 mg./l. up to under 500 mg./l. produces minimum tarnishing oroxidation of copper, cuprous alloy and silver surfaces or platedcoatings, that the decomposition of the cyanide complex in the solutionis very slow and may involve an hourly period. For example, a 100 mg./l.chlorine concentration produces a decomposition of the silver cyanidecomplex of only about 50%, using an hour of treatment. A 200 to 300mg./l. of chlorine concentration will decompose about of the complexwithin an hour. However, it has been discovered that it is necessary touse a much higher concentration of chlorine to assure decompositionwithin periods of a few minutes or less. Such rapid decomposition isimportant from the standpoint of safety of the operation, in that whenthe treated solution is to be recirculated from the treating tank it maybe returned for use again in the treatment tank. In this connection, thechange must be rapid enough to avoid cyanide drag-out from the treatmenttank and also insure faster flow through the treatment tank and tominimize any delay in flow from the reservoir tank. It is imperaturethat the cyanides be substantially completely destroyed or removed fromthe carry-over of the workpieces.

A heretofore limiting or offsetting factor as to the concentration ofthe chlorine or other treating chemical used, is that a freshly treatedor plated copper, cuprous alloy or silver surface is prone todiscoloration due to the oxidation as, for example, in a high chlorineconcentration solution. It has thus been necessary to limit the chlorinesolution concentration in the aqueous toxic removing or neutralizingsolution for workpieces having such a type of surface to under 500mg./l. and to under about mg./l. of chlorine for silver surfaces. Evenunder such limitations and with some alloys difficulty was encountered,in that a slight tarnishing or darkening of the surfaces resulted withuneven oxidation leading to streakiness, etc.

It was discovered that the solution to the problem involved theprovision of a protective, corrosion or oxidation inhibiting coating,layer, or film on the bright surfaces of the workpieces that isimmediately or simultaneously applied thereto with the application ofthe neutralizing or toxic carry-over material removing solution.Contrary to what was expected, it was determined that such proectioncould be accomplished, employing the neutralizing solution as thecarrying agency, irrespective of whether the carry-over on theworkpieces is of acyanide or an acid solution type, without adverselyeffecting the desired reactions of the neutralizing or treating solutionchemicals, and without adverse reactions with either the treatingsolutionchemicals or the reaction products produced with the toxiccarry-over. It was also discovered that contrary to expectations, such aprotective film will be retained on the workpieces even after they leavethe treating solution bath and while they are moved or advanced to awashing water rinse. The latter is highly desirable in that it has beendetermined that the bright surfaces of the workpieces are sensitive toair oxidation immediately after removal of the toxic carry-over. It wasdiscovered that an organic inhibitor could be employed toelectro-chemically form an organo-metallic monomolecular layer of film.Such a film is extremely thin and will tie down and immobilize metalions that would normally tend to combine with oxidizing elements in thetreating solution or the air. Such an inhibitor will be effective evenin a treating solution of a relatively high pH and even when thesolution is heated to a temperature within a range of about 120 to 212F.

As to toxic cyanide carry-over of the workpieces, it has been found thata range of chlorine concentration of over about 500 to about 2000 mg./l.or an optimum of about 1000 to 1500 mg./l. may be successfully employedto accomplish a complete reaction with the cyanide, within a period ofapproximately to minutes, and that the surfaces will be inhibited orprotected from streaks, tarnishing or oxidation by employing a stableorganic inhibiting chemical, e.g., 1, 2, 3 benzotriazole, C H NHNbenzene azimide, in the solution within a concentration range of .01 to1 g./l. Such a chemical is not only stable in a chlorinated solution,but also in an alkaline solution employed to neutralize work emergingfrom an acid pickling, brightening, or plating solution, where theworkpieces are being subjected to a wash in a neutralizing treatmentsolution to which caustic soda and soda ash have been added and whichsolution may be operated at an elevated temperature. The inhibitorenables the full necessary concentrations of chlorine and otherchemicals without adversely effecting their reactions or slowing downthe processing.

In other words, an inhibitor such as 1, 2, 3 benzotriazole, allows anincreased range of treatment solution concentration, and limits orminimizes control requirements by widening the margin for safeoperation. It minimizes controls while, at the same time, leads tofaster oxidation of cuprous cyanide and silver cyanide solutioncomplexes that are normally slow in their decomposition.

It is well known that cyanide compounds, such as those of sodium,potassium, zinc or cadmium are decomposed in a matter of minutes, incomparison to those of copper, cuprous alloys and silver. It has beendiscovered that increasing the chlorine concentration in the treatmentsolution to hasten the oxidation reaction of the cyanide compounds willalso effect the tendency to oxidize the metallic surface carrying thetoxic chemical film solution that is to be broken down or neutralized.The oxidizing tendency of the chlorine in a chlorinated treatmentsolution or of the air when the metal surface is subjected to aneutralizing solution of high pH alkaline metal hydroxide, andespecially at an elevated temperature, is overcome by the protectionprovided by the inhibitor and the invisible organo-metallic compoundthat is formed in view of the inhibiting action described. The chemicalbreak-down of a cyanide solution is as follows:

As intimated, similar difficulties have been encountered in theproneness of copper and various cuprous alloys to oxidize under wastetreatment after acid processing. The conventional treatment has been torinse the workpieces after acid pickling, brightening or plating in aneutralizing solution containing caustic soda and soda ash, using areducing agent, such as sodium hydrosulfite (Na2S O to limit oxidationof the bright copper surface by air, by the caustic soda or by remainingoxidizing chemicals such as nitrates residual from a pickling process.To insure substantial freedom from oxidation, it has been foundnecessary to use sodium hydrosulfite at a concentration of about 500mg./l. and to maintain the caustic soda and soda ash content to yield apH of about 8 to 11. The copper salts dragged-in from the acidprocessing are then precipitated as cuprous oxide.

Sodium hydrosulfite is a relatively expensive chemical, costing at thepresent time in the neighborhood of about twenty-five cents per pound,and it is readily consumed due to the quantity of copper processed, andalso due to the fact that it is lost from oxidizing action of nitrateions and, with air, itself, as the solution is aerated.

Incorporating a chemical inhibitor in accordance with the presentinvention, enables the complete elimination of sodium hydrosulfite inthe make-up of the treating solution, to thereby greatly reduce thecost. An organic inhibitor chemical has been found to be relativelystable and to need only minimized replenishment, even in a continuousin-line process with treating solution recirculation, such ascontemplated. Using benzotriazole, caustic soda and soda ash may be madeup to yield a pH of 8 to 14 which is a much wider and more desirablerange than heretofore possible with sodium hydrosulfite and it is thuseasier to control. Benzotriazole is incorporated in the aqueous solutionin an effective working range of concentration of .10 to 1 g./ 1. Anoptimum range of this chemical in a treating solution after toxiccyanide or acid treating or processing has been found to be about .1 to.2 g./ 1. It produces a film on the workpieces that is invisible.

The toxic compounds under consideration, dealing with copper and silvertreating solutions, are the cyanides, such as alkali metal cyanides andmetal complex cyanides, such as cuprous cyanide, silver cyanide, andcyanides of zinc or nickel when treating copper alloys containing thesemetals. The cyanide, itself, is oxidized by the chlorination reaction.The copper becomes insoluble in a cuprous hydroxide or cuprous carbonateform. However, it is preferable that it become insoluble in the cupricoxide form. It has been determined that the latter will occur ifsufiicient chlorine is available to oxidize, not only the cyanide, butalso the copper ion, itself. A high chlorine concentration or a high pH,elevated temperature, caustic soda concentration accomplishes the sameresults. Cupric oxide is less soluble in water and is more inert whenthe solid waste is discarded, considering the possible toxic effect ofprecipitated sludges.

Another consideration is that cuprous cyanide by, itself, is insolubleas is silver cyanide. Such cyanide complexes are made soluble in asolution containing additional alkali metal cyanide compound. This meansthat for the dissolution of one mole of cuprous cyanide, an additionalmole of sodium or potassium cyanide is needed. The same is true withsilver cyanide. It has been determined that when oxidizing a chemicalsolution containing alkali metal cyanides and copper or silver cyanidecomplexes, the alkali metal cyanide may be decomposed with aninsufficient concentration of chlorine; and, in view of the loss ofalkali metal cyanide, cuprous cyanide will fall out as an insolublecompound in a precipitate. This same effect will also occur in a similarmanner with silver cyanide. In such a case, the cuprous or silvercyanide would remain as an insoluble solid in the sludge. Althoughreference has been made to insoluble cuprous cyanide and silver cyanide,the condition of insolubility is not an absolute one. Even though lessthan one mg./l. of cuprous or silver cyanide would be soluble in rainwater or in the river where the sludges may be carried, this range ofsolubility is still suflicient to create a toxic condition. Inaccordance with the invention, it is now practical to employ a highchlorine concentration in the treatment solution, without oxidizing thesurfaces of the work pieces, that is sufiicient to quickly oxidize andbreak-down the metal cyanide complexes before these can precipitate assparsely soluble but still toxic metal cyanides.

By employing the principles of the present invention, it is nowpractical to employ an in-line process, such as set forth in US. PatentNo. 3,218,254, for copper, copper a1- loy and silver surfacedworkpieces, without spoiling the brightness of the surfaces and evenwhen the treatingsolution is maintained at a relatively high pH and isheated to minimize the time required to accomplish a complete removal oftoxic carry-over.

I claim:

1. In an in-line process of treating copper, copper alloy and silversurfaces of workpieces that are sensitive to oxidizing discoloration forremoving toxic carry-over in the nature of toxic cyanide in solution,the steps of continuously-progressively advancing the workpieces withtoxic carry-over on their surfaces from a toxic chemical solutionapplying zone into and through a first treating zone for the toxiccarry-over and subsequently into and through a water washing secondzone; in the first treating zone, providing and maintaining an aqueoustoxic material neutralizing chemical solution having a pH of about 8 to14 and containing a pH promoting alkaline metal compound providing andmaintaining chlorine in a concentration of about 500 to 2000 mg./l. inthe neutralizing chemical solution of the first treatment zone, applyingthe aqueous chemical neutralizing solution directly to the toxiccarry-over on the workpieces under relatively high oxidizing conditionsin the first treating zone during their movement therethrough andsubstantially completely neutralizing the toxic carryover of theworkpieces in such zone, providing about .1 to 1 g./l. of benzotriazolein the aqueous chemical neutralizing solution and maintaining it in astable condition with respect to the chemical content of the solutionand to the content of the carry-over on the workpieces and to reactionthrough the second zone and while washing-01f their surfaces in thesecond zone.

2. In a process as defined in claim 1, maintaining the neutralizingchemical solution within a raised temperature of about 120 to 212 F. inthe first treating zone during the introduction into and movement of theworkpiece therethrough.

3..In a process as defined in claim 1, providing and maintaining thebenzotriazole in the neutralizing chemical solution within an optimumrange of .1 to .2 g./l.

4. In a process as defined in claim 1, providing and maintaining theaqueous toxic material chemical neutralizing solution with a pH of about11 to 14.

References Cited UNITED STATES PATENTS 2,257,133 9/1941 Shoemaker.

2,618,606 11/ 1952 Schaeifer 252137 2,725,314 11/1955 Lancy 134-15 XR2,830,942 4/1958 Elliot 134-29 XR 2,877,188 3/1959 Liddell 252-3892,941,953 6/1960 Hatch 212.7 XR 3,295,917 1/1967 Cotton 21-2.7 XR

MORRIS O. WOLK, Primary Examiner JOSEPH T. ZATARGA, Assistant ExaminerUS. Cl. X.R.

